Wing Bumps Make Shock Waves Less Of A Drag

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Wing Bumps Make Shock Waves Less Of A Drag

Boeing engineers are exploring how oscillating jets of air on a wing can reduce drag and increase flight speed or fuel efficiency during high-speed cruising, including flights approaching or exceeding the speed of sound.

The aircraft manufacturer revealed some of its research in a patent filing titled "Dynamic bumps for drag reduction at transonic-supersonic speeds." The idea is to use a grid of oscillating jets to weaken the shock waves produced when air passes over a swept wing at high speed, especially as planes reach Mach 0.8 .

"If you're looking out the window of a 737 and the sun is shining the right way, you can actually see the shock wave dancing over the top of the wing," John Croft, the Americas editor of FlightGlobal.com, told Wired.com. "That's a weak version of what would happen if you try to go faster."

Boeing claims the technology could cut drag by as much as 7.3 percent, which is significant in an era when aircraft manufacturers and airlines strive to increase fuel efficiency. And it's a key discovery because researchers have long tried to delay the onset of shock waves and weaken them when they occur.

Research by Airbus and others has shown strategically placed wing indentations and bumps can significantly reduce the shock wave that forms above it. Research by the University of Cambridge found rounded bumps on a transonic wing cut drag by as much as 30 percent. There's just one problem.

"The bumps were designed to work at one condition and one specific speed," Croft told us. "If you want to fly a different speed, you'll pay a penalty."

This is where Boeing's research comes in. The company hopes its can address the limitations of the fixed, or static, shock wave bumps by replacing them with virtual ones that can be adjusted as a plane changes speeds. This is how Croft explains it over at FlightGlobal:

The “dynamic bumps” system proposes a grid of oscillating jets, some that suck air and some that expel air, to create a recirculation pattern with magnitude and frequency that acts to weaken the normal shock wave by creating an oblique wave that acts to reduce aerofoil drag.

Croft says it's not clear when the research was conducted or what it says about Boeing's long term strategic plans.

Images: Boeing.

Boeing included these images in its patent application. The image above shows the oblique wave ahead of a shock wave and the dynamic bumps in cross section. The image below shows a typical location for the oscillating jets.